Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

detailed scientific experiments with nutrients, says, “We have repeatedly noticed that the symptoms were most obvious in the older leaves.” Sulfur deficiency resembles a nitrogen deficiency. Acute sulfur deficiency causes elongated stems that become woody at the base.
    Sulfur deficiency occurs indoors when the pH is too high or when there is excessive calcium present and available.
    Progression of deficiency symptoms at a glance:
    Similar to nitrogen deficiency: older leaves turn a pale green.
    Leaf stems turn purple and more leaves turn pale green.
    Entire leaves turn pale yellow.
    Interveinal yellowing occurs.
    Acute deficiency causes more and more leaves to develop purple leaf stems and yellow leaves.
    Treat deficiency by fertilizing with a hydroponic fertilizer that contains sulfur. Lower the pH to 5.5 to 6. Add inorganic sulfur to a fertilizer that contains magnesium sulfate (Epsom salts). Organic sources of sulfur include mushroom composts and most animal manures. Make sure to apply only well-rotted manures to avoid burning the roots.
    Toxicity: An excess of sulfur in the soil causes no problems if the EC is relatively low. At a high EC, the plants tend to take up more available sulfur which blocks uptake of other nutrients. Excess sulfur symptoms include overall smaller plant development and uniformly smaller, dark-green foliage. Leaf tips and margins could discolor and burn when severe.
    Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Check the pH of the drainage solution. Correct the input pH to 6. Severe problems require more water to be flushed through the growing medium. Flush a minimum of three times the volume of water for the volume of the growing medium.

Early stage of S deficiency.

Progression of S deficiency.

Later stage of S deficiency.
     
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MICRONUTRIENTS
    Zinc, iron, and manganese are the three most common micronutrients found deficient. Deficiencies of these three micronutrients plague many more grow rooms than I had imagined. Often deficiencies of all three occur concurrently, especially when the soil or water pH is above 6.5. Deficiencies are most common in arid climates–Spain, the Southwestern United States, Australia, etc.–with alkaline soil and water. All three have the same initial symptom of deficiency: interveinal chlorosis of young leaves. It is often difficult to distinguish which element–zinc, iron, or manganese–is deficient, and all three could be deficient. This is why treating the problem should include adding a chelated dose of all three nutrients.
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Micronutrients
    Micronutrients, also called trace elements or trace nutrients, are essential to chlorophyll formation and must be present in minute amounts. They function mainly as catalysts to the plant’s process and utilization of other elements. For best results, and to ensure a complete range of trace elements is available, use fertilizers designed for hydroponics. High quality hydroponic fertilizers use food-grade ingredients that are completely soluble and leave no residues. If using an inexpensive fertilizer that does not list a specific analysis for each trace element on the label, it’s a good idea to add soluble trace elements in a chelated form. Chelated micronutrients are available in powdered and liquid form. Add and thoroughly mix micronutrients into the growing medium before planting. Micronutrients are often impregnated in commercial potting soils and soilless mixes. Check the ingredients on the bag to ensure that the trace elements were added to the mix. Trace elements are necessary in minute amounts but can easily reach toxic levels. Always follow the manufacturer’s instructions to the letter when applying micronutrients, because they are easy to over-apply.
Zinc (Zn) - mobile
    Practical Information: Zinc is the most common micronutrient found deficient in arid climates and alkaline soils.
     
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    A chelate (Greek for claw) is an organic molecule that forms a claw-like bond with free electrically charged metal particles. This property keeps metal ions such as zinc, iron, and manganese, etc., soluble in water, and the chelated metal’s reactions with other materials is suppressed. Roots take in the chelated metals in a stable, soluble form that is used immediately.
    Natural chelates such as humic acid and citric acid can be added to organic soil mixes. Roots and bacteria also exude natural chelates to promote the uptake of